In automation—especially, in process automation—field devices are widely used that serve for the determination, optimization, and/or influencing of process variables. Sensors, such as level-measuring instruments, flow meters, pressure and temperature measuring instruments, conductivity meters, etc., which capture the corresponding process variables of level, flow, pressure, temperature, and conductivity, are used for the detection of process variables. Actuators, such as valves or pumps, are used to influence process variables and can be used to alter the flow of a fluid in a pipe section or the fill-level in a container. Field devices, in general, refer to all devices which are process-oriented and which provide or handle process-relevant information. In connection with the invention, field devices are thus understood to include remote I/O's (electrical interfaces), wireless adapters, or general devices that are arranged at the field level. A variety of such field devices are manufactured and marketed by the Endress+Hauser company. RFID systems are used, for example, to identify field devices.
An RFID system is made up of a transponder, which is located in a housing and contains a distinctive code, as well as a reader for reading this identifier. An NFC system additionally enables an opposite information path and, for example, the transmission of one or several measured values of a field device or an interconnection of multiple field devices. The disadvantage of RFID and NFC transponders is that the conductive housing of the field devices is essentially impermeable to electromagnetic waves in the range necessary for RFID.